Doctoral thesis, 2011

The first part of this thesis deals with long wavelength (1.2-1.3 um) InGaAs(N)
multiple quantum-well (QW) lasers grown on GaAs, with the aim of understanding
and improving their threshold and temperature characteristics. The epitaxial
material is grown by molecular beam epitaxy (MBE). By optimizing MBE growth
conditions we have obtained record low values for the threshold current density
of 107 and 133 A/cm^2/QW for triple QW 1.2 um InGaAs and 1.3 um GaInNAs
lasers, respectively. A thorough investigation of the temperature dependence of
the threshold current for ridge waveguide GaInNAs double QW lasers is presented.
The good temperature stability of GaInNAs lasers is usually attributed to a large
conduction band offset as well as strong defect recombination. This work, however,
reveals that their good temperature stability also to a large extent arises from a
significant and only weakly temperature dependent lateral diffusion current, which
is not an effect intrinsic to GaInNAs but rather related to the geometry of the laser
resonator.
The second part explores a concept used to engineer the spectral properties of
a semiconductor Fabry-Perot (FP) laser resonator. A wavelength dependent resonator
loss is obtained by introducing perturbations of the effective mode index at
key positions along the length of the FP resonator. In a spectrally engineered FP
resonator (SE-FPR) this is used to lower the resonator loss for selected longitudinal
modes which thereby require less gain for lasing. Previous treatments of SE-FPRs
generally relied on an approximation valid for a weakly perturbed resonator. This
work extends the treatment to also include strongly perturbed SE-FPRs. The design
and fabrication of SE-FPRs supporting either one or two selected modes are
investigated. For a strongly perturbed SE-FPR a very large reduction of the resonator
loss can be obtained for the selected modes, with the main feedback still
provided by the end facets. Fabrication tolerances are, however, strict; in particular
the positioning of the perturbations with respect to the end facets is critical.

single mode laser

transfer matrix method

threshold current

InGaAs

GaAs

multiple quantum wells

dilute nitrides

two-color laser

GaInNAs

Semiconductor lasers

molecular beam epitaxy

characteristic temperature

temperature dependence

ambipolar diusion

Fabry-Perot resonator

spectral engineering

Room A423 (Kollektorn) at the Department of Microtechnology and Nanoscience -- MC2

Opponent: Prof. Eoin O'Reilly, Tyndall National Institute at University College Cork, Ireland